The uncertainty in the dose calibration of high-energy radiation therapy accelerators using calibrated ionization chambers is on the order of plus or minus 5%. Many of the problems associated with ionization chambers do not exist for the Fricke ferrous sulfate dosimeter, however, the chemical yields, G values, for the Fricke dosimeter have similar uncertainties. It is proposed to determine the G values for the Fricke dosimeter for x rays and electrons in the energy range of 1-60 MeV. The resopnse of the Fricke dosimeter will be compared to that of an absorbed-dose calorimeter to be constructed from polystyrene so as to minimize uncertainty in the transfer of dose from the calorimeter to the dosimeter solution. A test calorimeter will also be constructed for measuring the thermal characteristics of each component of the absorbed-dose calorimeter prior to assembly.